What stomach/intestinal/colon problem could I be experiencing?

For the last couple of months I have experienced sharp/dull/achy pain on my lower left side abdomen, roughly 3 inches from my belly button. It is not constant, it happens once every two weeks or so. It will start off as light pain, then get severe. If I place a heating pad on it and sit still, the pain goes away. If I move and walk around, my pain starts back up. During the pain, I feel nauseous. Eventually the pain will go away. Another problem I have every once in awhile is blood in my stool. Could both these things be related? Any ideas what it could be?